Automation systems have been employed for mounting electronic components on a printed circuit board. Such automated mounting requires electronic components having flat terminals in place of leads, i.e. "leadless" electronic components, because positioning of electronic components having leads by machinery is difficult. Thus, techniques for modifying electronic components with leads to "leadless" components have been developed.
A cylindrical aluminum electrolytic capacitor essentially has a structure in which two leads extend from one end of the capacitor. Some references disclose a cylindrical aluminum electrolytic capacitor device having flat terminals suitable for mounting on a printed Circuit board in which an insulating mounting board is attached to a bottom surface of a capacitor. The insulating mounting board is square or generally square with a side substantially as long as the diameter of a cylindrical casing of the capacitor.
For example, Japanese Unexamined Patent Publication (KOKAI) No. SHO 59-211213 discloses a cylindrical aluminum electrolytic capacitor device in which two leads of a capacitor respectively are inserted to extend through two openings in a mounting board, and are so bent as to locate in two respective grooves formed In the outward facing (bottom) surface of the mounting board. The bent portions of the leads are used as terminals to be soldered to conductors on a printed circuit board.
Japanese Examined Utility Model Publication (KOKOKU) No. HEI 3-25393 discloses that the bottom surface of a mounting board is provided with metallic terminal members having grooves in which bent portions of leads are placed, and the bent portions are soldered to the metallic terminal members in the grooves.
Such prior arts, however, have disadvantages, Leads must be bent at the right angle at the exits of respective openings in a mounting board. When the leads are bent, they are pulled, which may result in poor connection to electrodes in a casing. For reducing the tension to the leads, the leads each may be provided with a notch at a location at which that lead is to be bent. Such notches, however, reduce mechanical strength of the leads, which may cause the leads to be cut at the notches by vibrations or shocks.
In addition, it is difficult to insert the leads through the openings by using machinery. Failure in inserting the leads through the openings causes the leads to be caught between the bottom surface of the capacitor and the inner (top) surface of the mounting board. Such leads cannot form terminals for connection to a printed circuit board. Capacitors and mounting boards between which one of leads remains caught are joined together by the other lead which is successfully inserted into the opening and in engagement with the mounting board may be supplied as superficially complete capacitor devices.
Japanese Unexamined Patent Publication (KOKAI) No. SHO 62-186519 discloses a technique to eliminate the necessity of bending leads. According to this technique, openings in a mounting board have a larger diameter on its side facing a capacitor than on its outward facing surface. Short leads of the capacitor are inserted into the openings and the tip ends of the leads are connected to metallic terminal members on the outward facing surface of the mounting board.
This technique, however, does not completely eliminate difficulty in inserting the leads into the openings in the mounting board, and the strength of connection between the leads and the metallic terminal members is not sufficient.
An object of the present invention is to provide an improved "leadless" electronic device, e.g. a "leadless" aluminum electrolytic capacitor device, including an electronic component and a mounting board connected to the electronic component. A capacitor device according to the present invention is free from the disadvantages stated above and can be manufactured by an automation system without need for inserting leads of a capacitor through small openings in a capacitor mounting board.